The Use of a Diagnostic and Predictive Tool in Geography: A Simulation of Blister Rust Diffusion

The Use of a Diagnostic and Predictive Tool in Geography: A Simulation of Blister Rust Diffusion Richard G. Silvernail University of South Carolina The geographer is concerned with a point of view that is spatial in nature. As Berry has noted, "The integrating concepts and processes of the geographer relate to spatial arrangements and organization, and to spatial process." (1) The ability of the geographer to describe, record, and analyze in this context is well-established, but to confine ourselves to this is to miss an opportunity to make a further contribution. We should also endeavor to predict future spatial relationships, assuming we have done a thorough job of collecting and analyzing the raw data, and assuming we have mastered certain tools of analysis. In this context "future" is taken to mean a limited time period beyond the present. One tool or technique is known as the simulation of diffusion. While a rather elementary tool, it can nevertheless allow us to predict in a general manner. It can be useful not only in predicting spatial patterns, but also in diagnosing or testing relationships at the theoretical level. It should be noted that there are many types of simulation employed both in the physical and in the social sciences. Electric analogs and cloud chambers have long been used in physics. Simulation of diffusion has been used in rural sociology and agricultural economics for some time. The simulation type that is utilized in this paper is the Monte Carlo technique of simulation . In this paper an example is drawn from the field of resource management in an attempt to show the dual usefulness of simulation. Specifically, this paper will examine a simulation of blister-rust diffusion. Blister rust, a parasitic fungus disease (Cronartium rihicola, Fischer), kills more white pine in the United States than any other disease. The rust was introduced into the United States in 1909 and has since spread into the New England, Middle Atlantic, and Northern Great Lakes states. By the Lea Act of 1940, the United States Forest Service is responsible for leadership, coordination, and technical direction of rust control activities in forest land of all types of ownership. The service is responsible for estimating the total amount of public funds which should be invested in blister rust control. An inherent responsibility of the Forest Service is the investment of available rust control funds in areas that will return the greatest benefit. At present, the basis for allocation of funds is the amount of timber in pine stands in a given hazard area. For one-half century, the requirements for the spread of blister rust were 42The Southeastern Geographer intuitively thought to be elements of the physical environment. Charlton (2) developed a technique which assigned probability percentages to various elements of weather and topography which were deemed important in the spread of the disease. It should be noted that these probability percentages do not constitute an empirically derived formula, but are based on the intuition of an experienced and capable field man. If left at this point, Charlton's formula would remain merely an interesting hypothesis, untested and untried. This situation is not unknown in geographic research. A capable, experienced worker, faced with a problem in his area or specialty , may intuitively feel what he considers to be the correct approach. However, if his intuition remains untested, there would be a modicum of doubt and his readers certainly would qualify their acceptance of his statements. This case study does not purport to introduce new facts about blister rust, but rather it will attempt to test a theoretical formula evolved by an expert in the field of plant disease. If the formula is proven statistically significant, then Charlton's generalized hazard zones can be accepted as a basis for initial allocation of funds; i.e., the high-hazard zone should be the first to receive monies for disease prevention. A by-product of successful testing would be a specific rather than generalized hazard zone map which in turn would enable a priority system to be established. The priority system would allocate available monies to give the most effective coverage possible . THE DISEASE. As a parasitic fungus, blister rust exists...